1. Field of the Invention
The present invention relates to an apparatus and methods for facilitating the connection of tubulars. More particularly, the invention relates to an interlock system for a ton drive and a snider for use in assembling or disassembling tubulars.
2. Background of the Related Art
In the construction and completion of oil or gas wells, a drilling rig is constructed on the earth's surface to facilitate the insertion and removal of tubular strings into a wellbore. The drilling rig includes a platform and power tools such as an elevator and a spider to engage, assemble, and lower the tubulars into the wellbore. The elevator is suspended above the platform by a draw works that can raise or lower the elevator in relation to the floor of the rig. The spider is mounted in the platform floor. The elevator and spider both have slips that are capable of engaging and releasing a tubular, and are designed to work in tandem. Generally, the spider holds a tubular or tubular string that extends into the wellbore from the platform. The elevator engages a new tubular and aligns it over the tubular being held by the spider. A power tong and a spinner are then used to thread the upper and lower tubulars together. Once the tubulars are joined, the spider disengages the tubular string and the elevator lowers the tubular string through the spider until the elevator and spider are at a predetermined distance from each other. The spider then re-engages the tubular string and the elevator disengages the string and repeats the process. This sequence applies to assembling tubulars for the purpose of drilling a wellbore, running casing to line the wellbore, or running wellbore components into the well. The sequence can be reversed to disassemble the tubular string.
During the drilling of a wellbore, a drill string is made up and is then necessarily rotated in order to drill. Historically, a drilling platform includes a rotary table and a gear to turn the table. In operation, the drill string is lowered by an elevator into the rotary table and held in place by a spider. A Kelly is then threaded to the string and the rotary table is rotated, causing the Kelly and the drill string to rotate. After thirty feet or so of drilling, the Kelly and a section of the string are lifted out of the wellbore, and additional drill string is added.
The process of drilling with a Kelly is expensive due to the amount of time required to remove the Kelly, add drill string, reengage the Kelly, and rotate the drill string. In order to address these problems, top drives were developed.
For example, International Application Number PCT/GB99/02203, published on Feb. 3, 2000 discloses apparatus and methods for connecting tubulars using a top drive. In another example, FIG. 1 shows a drilling rig 100 configured to connect and run casings into a newly formed wellbore 180 to line the walls thereof. As shown, the rig 100 includes a top drive 200, an elevator 120, and a spider 400. The rig 100 is built at the surface 170 of the well. The rig 100 includes a traveling block 110 that is suspended by wires 150 from draw works 105 and holds the top drive 200. The top drive 200 has a gripping means 301 for engaging the inner wall of the casing 15 and a motor 240 to rotate the casing 15. The motor 240 may rotate and thread the casing 15 into the casing string 16 held by the spider 400. The gripping means 301 facilitate the engagement and disengagement of the casing 15 without having to thread and unthread the casing 15 to the top drive 200. Additionally, the top drive 200 is coupled to a railing system 140. The railing system 140 prevents the top drive 200 from rotational movement during rotation of the casing string 16, but allows for vertical movement of the top drive 200 under the traveling block 110.
In FIG. 1, the top drive 200 is shown engaged to casing 15. The casing 15 is placed in position below the top drive 200 by the elevator 120 in order for the top drive 200 to engage the casing 15. Additionally, the spider 400, disposed on the platform 160, is shown engaged around a casing string 16 that extends into wellbore 180. Once the casing 15 is positioned above the casing string 16, the top drive 200 can lower and thread the casing 15 into the casing string 16, thereby extending the length of the casing string 16. Thereafter, the extended casing string 16 may be lowered into the wellbore 180.
FIG. 2 illustrates the top drive 200 engaged to the casing string 16 after the casing string 16 has been lowered through a spider 400. The spider 400 is shown disposed on the platform 160. The spider 400 comprises a slip assembly 440 including a set of slips 410 and piston 420. The slips 410 are wedge-shaped and constructed and arranged to slidably move along a sloped inner wall of the slip assembly 440. The slips 410 are raised or lowered by the piston 420. When the slips 410 are in the lowered position, they close around the outer surface of the casing string 16. The weight of the casing string 16 and the resulting friction between the casing string 16 and the slips 410 force the slips downward and inward, thereby tightening the grip on the casing string 16. When the slips 410 are in the raised position as shown, the slips 410 are opened and the casing string 16 is free to move axially in relation to the slips 410.
FIG. 3 is cross-sectional view of a top drive 200 and a casing 15. The top drive 200 includes a gripping means 301 having a cylindrical body 300, a wedge lock assembly 350, and slips 340 with teeth (not shown). The wedge lock assembly 350 and the slips 340 are disposed around the outer surface of the cylindrical body 300. The slips 340 are constructed and arranged to mechanically grip the inside of the casing 15. The slips 340 are threaded to piston 370 located in a hydraulic cylinder 310. The piston 370 is actuated by pressurized hydraulic fluid injected through fluid ports 320, 330. Additionally, springs 360 are located in the hydraulic cylinder 310 and are shown in a compressed state. When the piston 370 is actuated, the springs 360 decompress and assist the piston 370 in moving the slips 340 relative to the cylindrical body 300. The wedge lock assembly 350 is connected to the cylindrical body 300 and constructed and arranged to force the slips 340 against the inner wall of the casing 15.
In operation, the slips 340, and the wedge lock assembly 350 of top drive 200 are lowered inside the casing 15. Once the slips 340 are in the desired position within the casing 15, pressurized fluid is injected into the piston 370 through fluid port 320. The fluid actuates the piston 370, which forces the slips 340 towards the wedge lock assembly 350. The wedge lock assembly 350 functions to bias the slips 340 outwardly as the slips 340 are slidably forced along the outer surface of the assembly 350, thereby forcing the slips 340 to engage the inner wall of the casing 15.
FIG. 4 illustrates a cross-sectional view of a top drive 200 engaged to the casing 15. Particularly, the figure shows the slips 340 engaged with the inner wall of the casing 15 and a spring 360 in the decompressed state. In the event of a hydraulic fluid failure, the springs 360 can bias the piston 370 to keep the slips 340 in the engaged position, thereby providing an additional safety feature to prevent inadvertent release of the casing string 16. Once the slips 340 are engaged with the casing 15, the top drive 200 can be raised along with the cylindrical body 300. By raising the body 300, the wedge lock assembly 350 will further bias the slips 340 outward. With the casing 15 retained by the top drive 200, the top drive 200 may relocate the casing 15 to align and thread the casing 15 with casing string 16.
In another embodiment (not shown), a top drive includes a gripping means for engaging a casing on the outer surface. For example, the slips of the gripping means can be arranged to grip on the outer surface of the casing, preferably gripping under the collar of the casing. In operation, the top drive is positioned over the desired casing. The slips are then lowered by the top drive to engage the collar of the casing. Once the slips are positioned beneath the collar, the piston is actuated to cause the slips to grip the outer surface of the casing.
FIG. 5 is a flow chart illustrating a typical operation of running casing using a top drive 200 and a spider 400. The flow chart relates to the operation of an apparatus generally illustrated in FIG. 1. At a first step 500, a casing string 16 is retained in a closed spider 400 and is thereby prevented from moving in an axial direction. At step 510, top drive 200 is moved to engage a casing 15 with the aid of an elevator 120. Engagement of the casing 15 by the top drive 200 includes grasping the casing 15 and engaging the inner surface thereof. At step 520, the top drive 200 moves the casing 15 into position above the casing string 16 for connection therewith. At step 530, the top drive 200 threads the casing 15 to casing string 16. At step 540, the spider 400 is opened and disengages the casing string 16. At step 550, the top drive 200 lowers the extended casing string 16 through the opened spider 400. At step 560, the spider 400 is closed around the casing string 16. At step 570, the top drive 200 disengages the casing string 16 and can proceed to add another casing 15 to the casing string 16 as in step 510. The above-described steps may be utilized to run drill string in a drilling operation, to run casing to reinforce the wellbore, or to assemble run-in strings to place wellbore components in the wellbore. The steps may also be reversed in order to disassemble a tubular string.
Although the top drive is a good alternative to the Kelly and rotary table, the possibility of inadvertently dropping a casing string into the wellbore exists. As noted above, a top drive and spider must work in tandem, that is, at least one of them must engage the casing string at any given time during casing assembly. Typically, an operator located on the platform controls the top drive and the spider with manually operated levers that control fluid power to the slips that cause the top drive and spider to retain a casing string. At any given time, an operator can inadvertently drop the casing string by moving the wrong lever. Conventional interlocking systems have been developed and used with elevator/spider systems to address this problem, but there remains a need for a workable interlock system usable with a top drive/spider system such as the one described herein.
There is a need therefore, for an interlock system for use with a top drive and spider to prevent inadvertent release of a tubular string. There is a further need for an interlock system to prevent the inadvertent dropping of a tubular or tubular string into a wellbore. There is also a need for an interlock system that prevents a spider or a top drive from disengaging a tubular string until the other component has engaged the tubular.